severe idle problem - one month later...solved!!!

[falcon fanatic]

Well, it seems everyone was right in a way: it was both a vacuum leak, and a problem with the carb. Allow me to quote the rebuilder from Top-End performance:

"James,

Your DGS blew out a sealing plug on an internal passageway....so the vacuum leak you were searching for was coming from the actual carb body. I should have it repaired and on the way back to you in about a week."

In response to my further queries:
"A backfire could never blow the plug out it basically had to wriggle out over time or melt if the carb was subjected to intense heat…weber leaded the holes left over after the internal passages were machined in these carbs. It is a clean hole so my theory is that it just popped out. I will seal it with epoxy instead of lead so you will never have this problem again. "

 

[falcon fanatic]

Allright, it's been nearly a month now and I still can't fix this thing. I now have a holley/weber from stovebolt as an interim carb. I've removed and replaced the carb and all adapters several times. This morning I made all new gaskets, cleaned everything meticulously, reassembled with gaskacinch, and the problem is exactly the same. The thing is, I've been through one and a half cans of starter fluid trying to find this vacuum leak, and no joy.

Now the interesting part. I can get the car to idle down to about 1600 rpm. Then the tach needle starts to go crazy. It falls to zero, and then flops around a bit, and then the car dies with a huff. The tach is wired directly to my DUI ignition, and this tach has always been rock steady, up until this problem started. Am I having an ignition problem? If so, what? As much as I like my DUI ignition, if the problem is with the ignition, this will be the second one of these that I've had problems with.

 

[Bort62]

Sounds like you have a miss at low RPM.

Burned valve?

 

[falcon fanatic]

Doubt it's a burned valve. Brand new head with only about 25 miles on it, stainless valves. At 1600 rpm it runs smooth as can be. At 1500 it dies like someone pulled the plug.

 

[Bort62]

Okay, well - what's the deal with your ignition system? oil on your plugs ?

If the tach is jumping around at low RPM, it's cause it's missing. A real bad miss at low RPM can be all sorts of things, but typically electrical.

 

[Bort62]

I should also throw out there, it could be missing because of a big vac leak and its just stumbling.

What sorta vac accessories do you have ?

 

[falcon fanatic]

I'm sort of discarding the vac leak at this point since I've tried all the usual ways of finding it. I've even disconnected all my vac accessories (only distributor, and brakes and trans off the same tee) and plugged them.

BEcause of the abrupt nature of the problem and the way the tach is acting, I am leaning towards ignition. I'll talk to perfomrance distributor in the morning.

 

[Bort62]

Do you have an inductive timing light ?

If so - you can use it to figure out which hole is missing. Put the light's pickup on each plug wire. The light should flash regularly, it directly correlates to when your spark is firing. If the light is intermittent or irregular in any way, it means you spark is too.

If you have a plug not firing all the time, it will show up in the light really clearly.

 

[fphillips]

Have you done a compression test since this problem started?

I had two cylinders with broken rings and it would die under 2000 rpm. Incidentally, I also was running weber/DUI, but the rings were the problem.

 

[falcon fanatic]

I like the timing light idea. Obvious, but I hadn't thought of it. No to the compression test. my tester was stolen along with all my other tools last summer and I haven't replaced it yet.

 

[falcon fanatic]

Bad module on the DUI. Ran down to Auto Zone and picked up a $16 replacement on a suggestion from Mike. Dropped it in and voila, car runs great. Now I just need to get a replacement hipo unit from Performance Distributor and I'll be back to 100%. Plus, I now have two carbs to play with: a 38/38 and a 32/36. I should get a 34/34 just so I have the whole set!

I'm very happy at this moment.

Wondering about the reliability of these DUI pieces, though. Everybody else seems to fine with them, so maybe the fact that my coil was shorting damaged the module. I'm guessing they didn't replace it, though I would assume they did a total overhaul when I sent it in for repair.

 

[Bort62]

I have seen a few members on this forum with DUI reliability problems.

Ill stick with my duraspark. Cheaper - same performance, and factory reliable

It's funny 'cause all the GM guys go away from the coil-in-cap HEI to a divorced coil setup, and everyone else seems to want to go to the coil-in-cap design.

Grass is always greener I suppose.

 

[XFlow_Fairlane]

I'll stick iwith my EEC4 dizzy.....had to replace a mod on it...but it did also come from a JY so who knows.